The invention relates to improved method and apparatus for introducing gasses for dissolution into liquid. This is when gasses are utilized in the treatment of aqueous liquid as is well-known. Generally known as diffuser, aerator, or sparger apparatus, improvement shown herein attains substantially more effective attainment of the object of various gas treatments of liquid. Apparatus of the type referred to and which is improved as shown herein is represented by U.S. Pat. Nos. 3,977,606, 4,007,240, 3,953,553, 4,093,681, 3,575,350, 4,022,854 and 3,857,910.
In addition to the gaseous treatment of liquids in pools or tanks by carbon dioxide or chlorination for example, artificial aeration is well known as means for introducing dissolved oxygen into water. Such aeration has the object of increasing the oxygen content of aqueous systems of water management. These systems are those with quality impaired stemming from use in commercial fishery operation or amateur aquaria use, the discharge of industrial waste in streams and lagoons such as by petrochemical or paper plants, the massive impairment of water quality and the pollution thereof stemming from necessary usage in municipal sewage systems.
The prior art has addressed itself to the problems of achieving effective gas dissolution in liquid essentially by the utilization of conduit-connected perforated tubing positioned under liquid. With gas introduced into the conduit the tubing is able to release the gas, the dissolution of which is desired in the liquid, as a myriad of small bubbles. Such apparatus is conventionally known as diffuser, gas aerator, or sparger apparatus. Frequently the perforated tubing portion of the apparatus is comprised of fritted glass, sintered polymer granules compressed into a gas permeable conduit for gas, or any suitable gas permeable material able to conduct and release gas into liquid forming a myriad of small bubbles therein.
Albeit the recognized utility of gas treatment and aerating means in water management, methods related thereto such as the above have not been wholly satisfactory. This is because of low efficiency in dissolution or absorption requiring high gas input requirements with much waste of the gas introduced. Biochemical oxygenation employs air as the oxygen source utilizing large quantities thereof, because of such waste, with substantial power required. This is in providing the excess quantities needed for required dissolution of oxygen in the water being treated.
The prior art has long sought to improve gas-liquid contacting techniques by means employing agitated gas-liquid columns, plate-type columns, mechanical mixing in combination with diffusers, multiple gas contact tanks in series, the use of temperature and pressure to aid gas dissolution. However there has been no system of gas transfer in water management that may be considered substantially the superior of known prior art methods such as those above.
The difficulty of efficient gas-liquor transfer in large water management systems may be appreciated, for example, by reference to small scale amateur aquaria. Here air pumps are commonly utilized to introduce air as a source of oxygen to aquaria water containing fish. The utility of the introduced oxygen is maintenance of water quality by biochemical oxidation of the nitrite content of the water stemming from considerable waste discharged by fish. Levels of 0.1 mg N/liter (ppm) represent satisfactory water condition otherwise fish will lack appetite, have closed fins, be susceptible to disease, and succumb to higher levels of nitrite concentration they cannot tolerate. it was believed at one time that the rising bubbles from artificial aeration as practised in aquaria and similar wastewater treatment systems totally dissolved as they rose in the water. However it is now known that this is untrue. Such bubbling essentially merely moves water to the surface. Most of the oxygenation in such systems occurs at the air-water interface from the exposure of the water surface to air. This represents inefficient and poor attainment of objectives in water quality management.